Optical recording medium for checking compatibility of an optical pickup device and method of checking an optical pickup device using the same

ABSTRACT

Two or three different signal recording regions are formed in one optical disk. One signal recording region is positioned at a depth of 0.6 mm from a disk surface and is formatted in accordance with a single layer or two layer DVD standard, for example. Remaining signal recording region is positioned at a depth of 1.2 mm from the disk surface and is formatted in accordance with the CD, CD-R or MO disk standard, for example. By using such an optical disk, whether a manufactured optical pickup device is capable of reproducing two or three different types of optical disks can be checked quickly.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical recording medium forchecking compatibility of an optical pickup device and to a method ofchecking an optical pickup device using the same. More particularly, thepresent invention relates to an optical disk for checking whether anoptical pickup device is capable of reproducing signals of a pluralityof optical disks of different standards, and to a method of checking.

2. Description of the Background Art

An optical disk having the thickness of about 1.2 mm from which signalsare read by using a semiconductor laser, such as a CD-ROM (CompactDisk-Read Only Memory) has been proposed. In order to read a signal fromthis type of optical disk, an objective lens for pickup is controlled inaccordance with focus and tracking servo while pit string on a signalrecording surface is irradiated with a laser beam.

Recently, density has been made higher to record motion picture for along period of time. For example, a DVD (Digital Video Disk) standardhas been proposed for recording about 5G byte of signals on one surfaceof an optical disk having the diameter of 12 cm which is the same as anordinary CD-ROM. The substrate for the DVD is about 0.6 mm in thickness,and by adhering two such disks as one and the other surfaces, it ispossible to record about 10G byte of signals in one DVD.

Accordingly, in the future, there will be optical disks having thinsubstrate of 0.6 mm in thickness and optical disks having standardsubstrate of 1.2 mm in thickness existing together.

Japanese Patent Laying-Open No. 5-303766 discloses an optical pickupdevice which is capable of reproducing both the high density opticaldisk having the thin substrate of 0.6 mm in thickness and the standarddensity optical disk having the standard substrate of 1.2 mm inthickness.

In the situation where optical disks having the thicknesses of 0.6 mmand 1.2 mm exist together, it is most important that an optical pickupdevice is capable of reproducing a CD (Compact Disk), a CD-R (CompactDisk-Recordable), a DVD and an MO (Magneto-Optical) disk. Accordingly,an optical pickup device has been developed which is compatible inreproducing 1) CD and DVD, 2) CD-R and DVD, 3) MO disk and DVD, 4) CD,CD-R and DVD, and 5) CD, MO disk and DVD. Therefore, in manufacturingsuch pickup devices, it is necessary to quickly check whether theoptical pickup device has desired compatibility.

SUMMARY OF THE INVENTION

Therefore, the object of the present invention is to provide an opticalrecording medium for enabling quick checking of compatibility of anoptical pickup device.

Another object of the present invention is to provide a method ofchecking compatibility of an optical pickup device using the opticalrecording medium.

According to an aspect of the present invention, the optical recordingmedium includes a transparent substrate, a first signal recordingregion, a first reflection film, a second signal recording region and asecond reflection film. The transparent substrate has a main surface.The first signal recording region is formed substantially parallel tothe main surface in the transparent substrate, and is formatted inaccordance with a first standard. The first reflection film is formed onthe opposite side of the main surface of the transparent substrate onthe first signal recording region. The second recording region is formedin the transparent substrate substantially parallel to the main surfaceof the substrate, and is formatted in accordance with a second standard.The second reflection film is formed on the opposite side of the mainsurface of the transparent substrate on the second signal recordingregion.

Preferably, distance between the first signal recording region and themain surface of the transparent substrate is shorter than distancebetween the second signal recording region and the main surface of thetransparent substrate.

More preferably, the first signal recording region is formed partiallyin the transparent substrate. The second signal recording region isformed entirely in the transparent substrate.

Preferably, the transparent substrate is formed of glass.

According to another aspect of the present invention, the opticalrecording medium includes a first transparent substrate, a first signalrecording region, a first reflection film, a second transparentsubstrate, a second signal recording region and a second reflectionfilm. The first signal recording region is formed on the firsttransparent substrate and is formatted in accordance with a firststandard. The first reflection film is formed on the first signalrecording region. The second transparent substrate is formed on thefirst transparent film. The second signal recording region is formed onthe second transparent region.

According to a still another object of the present invention, the methodof checking an aforementioned optical recording medium includes thesteps of irradiating a first signal recording region with a laser beamfrom an optical pickup device, to determine if the optical pickup deviceis capable of reproducing a signal from the first signal recordingregion; after the step of determination, moving the optical pickupdevice from the first recording region to the second recording region;after the step of moving, irradiating the second signal recording regionwith a laser beam from the optical pickup device to determine whether ornot the optical pickup device is capable of reproducing a signal fromthe second signal recording region.

An advantage of the present invention is that compatibility of theoptical pickup device can be checked quickly as one optical recordingmedium has a plurality of signal recording regions which are formattedin accordance with mutually different standards.

Another advantage of the present invention is that the optical recordingmedium has high durability against frequent use for checking, as thetransparent substrate is formed of glass.

A still further advantage of the present invention is that adjustment ofthe optical pickup device can be performed with high precision sincethere is hardly a warp or surface vibration.

The foregoing and other objects, features, aspects and advantages of thepresent invention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing an overall structure of an opticaldisk reproducing apparatus including a DVD/CD compatible optical pickupdevice.

FIG. 2 is a block diagram showing an optical system of the opticalpickup device shown in FIG. 1.

FIG. 3 is a side view of a polarization selecting unit shown in FIG. 2.

FIG. 4 is a front view of the polarization selecting unit shown in FIG.3.

FIG. 5 is a cross section showing a structure of an optical disk inaccordance with a first embodiment of the present invention.

FIG. 6 is a plan view of the optical disk shown in FIG. 5.

FIG. 7 is an illustration showing the method of checking compatibilityof the optical pickup device using the optical disk shown in FIGS. 5 and6.

FIGS. 8 to 15 are cross sections showing structures of optical disks inaccordance with the second to ninth embodiments of the presentinvention.

FIG. 16 is a block diagram showing an optical system of a DVD/CD-Rcompatible optical pickup device.

FIG. 17 is a block diagram showing an optical system of a DVD/CD/CD-Rcompatible optical pickup device.

FIG. 18 is a cross sectional view showing a structure of an optical diskin accordance with a twelfth embodiment of the present invention.

FIG. 19 is a plan view of the optical disk shown in FIG. 18.

FIGS. 20 to 26 are cross sections showing structures of optical disks inaccordance with thirteenth to nineteenth embodiments of the presentinvention.

FIG. 27 is a block diagram showing an optical system of a DVD/CD/MOcompatible optical pickup device.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following, embodiments of the present invention will be describedin detail with reference to the figures. In the figures, same orcorresponding portions are denoted by the same reference characters anddescription thereof is not repeated.

First Embodiment

Table 1 below shows standards and conditions for reproduction of a DVD(Digital Video Disk) and a CD-DA (Compact Disk-Digital Audio;hereinafter simply referred to as "CD").

                  TABLE 1    ______________________________________    Type            DVD         CD    ______________________________________    Standard Substrate   0.6 mm      1.2 mm             Thickness   (0.55-0.65 mm)                                     (1.1-1.3 mm)             Shortest Pit                         0.40 μm  0.90 μm             Length     (0.3-0.5 μm)                                     (0.80-1.0 μm)             Track Pitch                         0.74 μm 1.6 μm                        (0.73-0.75 μm)                                    (1.5-1.7 μm)             Reflectance                        at     20-40% at least 70%                        least                        70%    Condition             Spot       0.9 μm   1.5 μm    for      Diameter   (0.85-0.95 μm)                                    (1.4-1.6 μm)    Reproduction             Numerical  0.60        0.42             Aperture   (0.55-0.65) (0.30-0.55)             Wavelength 635 nm                        (620-650 nm)    ______________________________________

As is apparent from the table, according to DVD standard, substratethickness is 0.6 (tolerance ±0.05) mm, shortest pitch length is 0.40(tolerance ±0.1) μm, and track pitch is 0.74 (tolerance ±0.01) μm. Onthe other hand, according to CD standard, substrate thickness is 1.2(tolerance ±0.1) mm, shortest pitch length is 0.9 (tolerance ±0.1) μmand track pitch is 1.6 (tolerance ±0.1) μm.

First, an optical disk reproducing apparatus including an optical pickupdevice capable of DVD and CD compatible reproduction will be described.Referring to FIG. 1, a reproduction signal detected from an optical disk11 by means of an optical pickup device 10 is applied to a preamplifier12. From preamplifier 12 to a determining portion 13, signals necessaryfor determining the optical disk such as a focus error signal areapplied, and at determining portion 13, optical disk 11 mounted on thereproducing apparatus is determined. The result of determination bydetermining portion 13 is applied to an instructing portion 14.Instructing portion 14 controls an NA switching portion 15 such thateffective numerical aperture (NA) of an objective lens in optical pickupdevice 10 is switched in accordance with the result of determinationfrom determining portion 13. NA switching portion 15 switches theeffective numerical aperture of the objective lens in accordance with aninstruction from instructing portion 13. The method of switchingeffective numerical aperture will be described later.

Instructing portion 14 also controls a circuit switching portion 16 inaccordance with the result of determination from determining portion 13.Circuit switching portion 16 switches an RF demodulating circuit 17 sothat it is suitable for reproducing the mounted optical disk 11. Thereproduction signal from preamplifier 21 is demodulated by RFdemodulating circuit 17. The reproduction signal from preamplifier 12 isalso applied to a servo circuit 18, and the servo circuit 18 controls aspindle motor 19 and so on for rotating optical disk 11.

Referring to FIG. 2, the optical pickup device 10 includes asemiconductor laser 20, a diffraction grating 21, a plane ofpolarization rotating unit 22 for rotating plane of polarization of thelaser beam, a half mirror 23, a collimator lens 24, a rising mirror 25,a polarization selecting unit 26 for intercepting only that laser beamwhich is polarized in a specific direction, an objective lens 29 forconverging laser beam to a signal recording surface 27 or 28 of anoptical disk 11, and a photodetector for detecting reflected light fromthe signal recording surface 27 or 28.

A plane of polarization rotating unit 22 includes a twisted nematicliquid crystal 31, and transparent electrodes 32, 32 for applying avoltage to liquid crystal 31. Objective lens 29 is designed such thatthe laser beam is focused on the signal recording surface 27 of the DVD,and has a numerical aperture of 0.6 (tolerance ±0.05).

Referring to FIG. 3, polarization selecting unit 26 includes aring-shaped polarization film 33, two transparent glass plates 34between which polarization film 33 is held, and a filter 35 adhered at acentral portion of glass plates 34 where polarization film 33 is absent.Filter 35 is to lower transmittance of the laser beam, and it does nothave any polarization selectivity. Polarization film 33 transmits onlysuch laser beam that is polarized in a specific direction. However, itstransmittance is about 70 to about 90%. Filter 35 is adhered on glassplate 34 so as to lower the transmittance of the central portion to thesame extent as that of the outer peripheral portion. In place oftransparent glass plate 34, a transparent body having superior opticalcharacteristics such as a plate formed of a resin such as polycarbonate,PMMA or the like may used.

Polarization characteristic of the polarization selecting unit 26 isshown by the arrows in FIG. 4. More specifically, at an outer peripheralportion 36 of polarization selecting unit 26, only that laser beam whichis polarized in a specific direction by polarizing film 33 istransmitted by about 70 to about 90%. Meanwhile, at the central portion37, laser beam polarizing in any direction is transmitted with similartransmittance (70-90%) as at the outer peripheral portion 36. In FIG. 4,only that laser beam which is polarized in the lateral direction istransmitted through the outer peripheral portion 36. Assuming that thenumerical aperture of objective lens 29 is 0.6 (tolerance ±0.05) andeffective beam diameter thereof is 4 mm, the diameter of the centralportion 37 is set to 2.3 (tolerance ±0.2) mm so that effective numericalaperture of objective lens 29 attains to 0.35 (tolerance ±0.05). Whenthe effective beam diameter is not 4 mm, the diameter of the centralportion 37 is set such that the effective numerical aperture of theobjective lens 29 attains 0.35.

Here, an operation of reproducing a DVD by optical pickup device 10shown in FIG. 2 will be described. When a DVD is to be reproduced, avoltage is applied to a transparent electrode 32 of plane ofpolarization rotating unit 22. As a result, laser beam polarized in adirection parallel to the sheet emitted from semiconductor laser 20enters plane of polarization rotating unit 22 through diffractiongrating 21, and it is transmitted as it is, with its plane ofpolarization not rotated by the plane of polarization rotating unit 22.The transmitted laser beam is reflected by half mirror 23, made parallelby a collimator lens 24 and reflected by a rising mirror 25 to bevertical with respect to the signal recording surface 27 or 28 ofoptical disk 11. The reflected laser beam enters polarization selectingunit 26, is entirely transmitted without being intercepted bypolarization selecting unit 26, and it enters objective lens 29. Theentered laser beam is condensed by objective lens 29 and directed tosignal recording surface 27 through transparent substrate 38 of the DVD.The laser beam reflected from signal recording surface 27 returnsthrough objective lens 29, polarization selecting unit 26, rising mirror25 and collimator lens 24 to half mirror 23. Half of the returning laserbeam is reflected by half mirror 23 and the remaining half is detectedby photodetector 30, whereby a reproduction signal is generated. Here,the spot diameter of the laser beam on signal recording surface 27 is0.9 (tolerance ±0.1) μm.

Meanwhile, when a CD is to be reproduced, voltage is not applied totransparent electrode 32 of plane of polarization rotating unit 22. As aresult, the laser beam polarized in a direction parallel to the sheetemitted from the semiconductor laser 20 enters the plane of polarizationrotating unit 22 through diffraction grating 21, and is transmitted withits plane of polarization rotated by 90° by plane of polarizationrotating unit 22. Consequently, the laser beam which has beentransmitted through plane of polarization rotating unit 22 is polarizedin a direction vertical to the sheet. The transmitted laser beam isreflected by half mirror 23, made parallel by collimator lens 24 andenters, through rising mirror 25, to the polarization selecting unit 26.Of the entering laser beam, outer peripheral portion is intercepted bypolarization selecting unit 26, and only the central portion istransmitted through polarization selecting unit 26. The laser beam(represented by the dotted line in FIG. 2) which has been transmittedthrough polarization selecting unit 26 is condensed by objective lens29, and is directed to the signal recording surface 28 throughtransparent substrate 39 of the CD. At this time, the outer peripheralportion of the laser beam is intercepted such that effective numericalaperture of objective lens 29 attains to 0.35 (tolerance ±0.05). Thespot diameter of the laser beam on the CD is 1.5 (tolerance ±0.1) μm.Except these, the operation is the same as described above, and hencedescription is not repeated.

In the foregoing, an example of a DVD/CD compatible optical pickupdevice has been described to show usefulness of the optical disk inaccordance with a first embodiment, which will be described later.However, the optical disk in accordance with the first embodiment is notlimited to the above described optical pickup device. It may be utilizedto check an optical pickup device which is capable of reproducing bothDVD and CD in accordance with other methods.

Now, it is necessary to check whether the optical pickup device 10structured as described above can actually reproduce both DVD and CD.However, it takes long time and prevents quick checking if a DVD and aCD are mounted on a reproducing apparatus in turn and respective opticaldisks are reproduced so as to check compatibility of the manufacturedoptical pickup device. The first embodiment allows checking of DVD andCD compatibility by using one optical disk.

Referring to FIG. 5, the optical disk in accordance with the firstembodiment includes a transparent substrate 42 formed of glass andhaving a main surface 41, a photo polymer (hereinafter referred to as"2P") ultraviolet curing resin 44 formed on transparent substrate 42 andhaving a signal recording region 43, a reflection film 45 formed ofaluminum on signal recording region 43, adhesion ultraviolet curingresin 46 formed on reflection film 45 and ultraviolet curing resin 44, atransparent substrate 45 formed of glass on ultraviolet curing resin 46,a 2P ultraviolet curing resin 49 formed on transparent substrate 47 andhaving a signal recording region, a reflection film 50 formed ofaluminum on CD signal recording region 48, and a protective film 51formed of a ultraviolet curing resin on reflection film 50. Reflectionfilm 45 may be formed of a metal, a metal oxide or a dielectric, otherthan aluminum.

Signal recording region 43 is formed substantially parallel to mainsurface 41 and is formatted in accordance with the DVD standard shown inTable 1. Therefore, in the following, this region will be referred to asa DVD signal recording region. Signal recording region 48 is formedsubstantially parallel to main surface 41 and is formatted in accordancewith the CD standard shown in Table 1. Therefore, in the following, thisregion will be referred to as a CD signal recording region. Distancebetween DVD signal recording region 43 and main surface 41 is 0.6(tolerance ±0.05) mm. Distance between CD signal recording region 48 andmain surface 41 is 1.2 (1.1-1.3) mm.

As shown in FIG. 6, DVD signal recording region 43 is formed on an outerperiphery of optical disk 40. CD signal recording region 48 is formedentirely over optical disk 40.

The thickness of reflection film 45 is set such that it has reflectanceof 20 to 40%. As for reflection film 50, it is set such that the filmhas reflectance not smaller than 70%.

In short, optical disk 40 is fabricated by adhering two optical diskseach having the thickness of 0.6 mm by ultraviolet curing resin 46, sothat signals can be reproduced both from the regions 43 and 48 withlaser beam irradiation from the side of main surface 41.

Next, the method of checking compatibility of the optical pickup device10 using optical disk 40 structured as above will be described. Opticaldisk 40 is mounted on a reproducing apparatus. Referring to FIG. 7, DVDsignal recording region 43 is irradiated with a laser beam from opticalpickup device 10, and whether optical pickup device 10 is capable ofcorrectly reproducing a signal from DVD signal recording region 43 isdetermined. After determination, optical pickup device 10 is moved fromDVD signal recording region 43 to CD signal recording region 48. Aftermovement, CD signal recording region 48 is irradiated with a laser beamfrom optical pickup device 10, and whether or not optical pickup device10 is capable of correctly reproducing a signal from CD signal recordingregion 48 is determined. Whether or not a correct reproduction signal isobtained is determined by detecting an eye pattern, a jitter or thelike, for example. As a result, when good reproduction signals areobtained both from signal recording regions 43 and 48, it is determinedthat optical pickup device 10 is capable of DVD and CD compatiblereproduction. Though a reproduction signal from DVD signal recordingregion 43 is checked first and thereafter reproduction signal from CDsignal recording region 48 is checked here, the reproduction signal fromCD signal recording region 48 may be checked first and the reproductionsignal from DVD signal recording region 43 may be checked thereafter.

As described above, according to the first embodiment, since opticaldisk 40 has signal recording region 43 formatted in accordance with theDVD standard and a signal recording region formatted in accordance withthe CD standard, compatibility of optical pickup device 10 can bechecked by using only one optical disk 40. Further, signals can bereproduced from both signal recording regions 43 and 48 by laserirradiation from one direction, it is not necessary to put the opticaldisk upside down during checking. As a result, time necessary forchecking can be significantly reduced.

Further, since CD signal recording region 48 is formed entirely over thesurface, patterning is not necessary, and therefore manufacturing stepis not complicated.

Further, since transparent substrate 42 is formed of glass, warp or thelike can be suppressed to the minimum even when optical disk 40 is usedfrequently for checking. Therefore, optical disk 40 has improveddurability.

Second Embodiment

Though DVD signal recording region 43 is formed on the outer peripheryof optical disk 40 in the first embodiment described above, it may beformed on an inner periphery of an optical disk 52 in accordance withthe second embodiment, as shown in FIG. 8.

Third Embodiment

Though DVD signal recording region 43 is formed partially in the firstand second embodiments above, it may be formed entirely over the surfaceof an optical disk 53 in accordance with a third embodiment, as shown inFIG. 9. Even when DVD signal recording region 43 is formed on the entiresurface, part of the laser beam is transmitted through DVD signalrecording region 43 and reaches CD signal recording region 48, as DVDsignal recording region has reflectance of 20 to 40%. Therefore, asignal from CD signal recording region 48 can be reproduced.

According to the third embodiment, signal recording regions 43 and 48 donot require patterning. Therefore, as compared with the first and secondembodiments, manufacturing steps can be simplified.

Fourth Embodiment

In the first to third embodiments above, CD signal recording region 48is formed over the entire surface of optical disks 40, 52 and 53.However, it may be formed only on the outer periphery of an optical disk54 as in the fourth embodiment shown in FIG. 10. In the secondembodiment shown in FIG. 8, CD signal recording region 48 is overlappedwith the DVD signal recording region 43 at the inner periphery ofoptical disk 52. However, the overlapped region is not necessaryinherently. Therefore, by patterning CD signal recording region 48, itmay be formed only on the outer periphery of optical disk 54 as shown inFIG. 10.

On the contrary, DVD signal recording region 43 may be formed only onthe outer periphery of the optical disk and CD signal recording region48 may be formed only on the inner periphery of the optical disk.

Fifth Embodiment

In the first embodiment above, transparent substrates 42 and 47 areformed of glass so as to improve durability. However, these may beformed of a polycarbonate resin as in the fifth embodiment shown in FIG.11. An optical disk 55 in accordance with the fifth embodiment includesa transparent substrate 56 formed of a polycarbonate resin having DVDsignal recording region 43 formed on the outer periphery, a protectionfilm 45 formed on DVD signal recording region 43, adhesion ultravioletcuring resin 46 formed on reflection film 45 and transparent substrate56, a transparent substrate 57 formed of a polycarbonate resin on resin46 and having CD signal recording region 48 formed on the entiresurface, a reflection film 50 formed on CD signal recording region 48,and protective film 51 formed on reflection film 50.

According to the fifth embodiment, since transparent substrates 56 and57 are formed of polycarbonate resin, DVD signal recording region 43 andCD signal recording region 48 can be directly formed on transparentsubstrates 56 and 57. As a result, optical disk 55 in accordance withthe fifth embodiment can be manufactured easier than optical disk 40 inaccordance with the first embodiment shown in FIG. 5.

Sixth Embodiment

The first to fifth embodiments above are directed to an optical disk forchecking single layer DVD and CD compatibility, while the sixthembodiment is directed to an optical disk for checking two layer DVD andCD compatibility.

Referring to FIG. 12, in an optical disk 58 in accordance with the sixthembodiment, the DVD signal recording region includes a first signalrecording layer 59, a transparent intermediate layer 62 formed on thefirst signal recording layer 59, and a second signal recording layer 60formed on transparent intermediate layer 62. The first signal recordinglayer 59 is formed on 2P ultraviolet curing resin 44. On the firstsignal recording layer 59, a semitransparent film 61 formed of gold,silicon carbide or the like is formed. Transparent intermediate layer 62is formed of 2P ultraviolet curing resin, on semitransparent film 61 andultraviolet curing resin 44. Transparent intermediate layer 62 has athickness of 10-20 μm. The second signal recording layer 62 is formed ontransparent intermediate layer 62. On the second signal recording layer62, reflection film 45 of aluminum is formed. Here, an adhesionultraviolet curing resin may be used in place of 2P ultraviolet curingresin of transparent intermediate layer 62 and a 2P ultraviolet curingresin may be used in place of adhesion ultraviolet curing resin 46.

By the optical disk 58 in accordance with the sixth embodiment, it ispossible to check two layer DVD and CD compatibility.

Seventh Embodiment

In the sixth embodiment above, the first and second signal recordinglayers 56 and 60 are formed on the outer periphery of optical disk 58.In the seventh embodiment shown in FIG. 13, the first and second signalrecording layers 59 and 60 are formed on the inner periphery of anoptical disk 63.

Eighth Embodiment

In optical disks 58 and 63 in accordance with the sixth and seventhembodiments above, outer diameter of the first signal recording layer 59is equal to the outer diameter of the second signal recording layer 60.In an optical disk 64 in accordance with the eighth embodiment shown inFIG. 14, outer diameter of the first signal recording layer 59 issmaller than that of the second signal recording layer 60. In thismanner, the first signal recording layer 59 may overlap not entirely butpartially with the second signal recording layer 60.

Ninth Embodiment

In the sixth embodiment shown in FIG. 12, transparent substrates 42 and47 are formed of glass. However, similar to the fifth embodiment shownin FIG. 11, in an optical disk 65 in accordance with a ninth embodimentshown in FIG. 15, transparent substrates 56 and 57 are formed ofpolycarbonate resin.

According to the ninth embodiment, the first signal recording layer 59is directly formed on transparent substrate 56 and the second signalrecording layer 60 and the CD signal recording region 48 are directlyformed on transparent substrate 57. Therefore, optical disk 65 can bemanufactured easier than optical disk 58 in accordance with the sixthembodiment.

Tenth Embodiment

In the first to ninth embodiments above, signal recording region 48 isformatted in accordance with the CD standard. Alternatively, it may beformatted in accordance with the CD-R (Compact Disk-Recordable)standard. Table 2 below shows standards and conditions for reproductionof DVD and CD-R.

                  TABLE 2    ______________________________________    Type            DVD         CD-R    ______________________________________    Standard Substrate   0.6 mm      1.2 mm             Thickness   (0.55-0.65 mm)                                     (1.1-1.3 mm)             Shortest Pit                         0.40 μm  0.90 μm             Length     (0.3-0.5 μm)                                     (0.80-1.0 μm)             Track Pitch                         0.74 μm 1.6 μm                        (0.73-0.75 μm)                                    (1.5-1.7 μm)             Reflectance                        at     20-40% at least                        least         60-70%                        70%    Condition             Spot       0.9 μm   1.5 μm    for      Diameter   (0.85-0.95 μm)                                    (1.4-1.6 μm)    Reproduction             Numerical  0.60        0.45             Aperture   (0.55-0.65) (0.40-0.50)             Wavelength 635 nm      780 nm                        (620-650 nm)                                    (765-795 nm)    ______________________________________

As is apparent from the table, CD-R standard is generally similar to CDstandard, except that the reflectance is higher than 60-70%. Further, alaser beam having the wavelength of 780 (tolerance ±15) nm is used forreproduction.

An example of an optical pickup device capable of reproducing both DVDand CD-R will be described. Different from DVD/CD compatible opticalpickup device 10 shown in FIG. 2, a DVD/CD-R compatible optical pickupdevice 66 shown in FIG. 16 includes a semiconductor laser 69 whichinclude a laser element 67 for generating a laser beam having thewavelength of 635 (tolerance ±15) nm and a laser element 68 forgenerating a laser beam having the wavelength of 780 (tolerance ±15) nm.Optical pickup device 66 includes two objective lenses 70 and 71.Objective lens 70 is designed for DVD and has numerical aperture of 0.6(tolerance ±0.05). Objective lens 71 is designed for CD-R and hasnumerical aperture of 0.45 (tolerance ±0.05). Objective lenses 70 and 71are switched in accordance with the optical disk to be reproduced (DVDor CD-R).

When a DVD is reproduced, laser element 67 is activated and objectivelens 70 is moved to a prescribed position. Consequently, laser beamhaving the wavelength of 635 nm emitted from laser element 67 passesthrough objective lens 70 and is focused on DVD signal recording surface27.

Meanwhile, when a CD-R is reproduced, laser element 68 is activated andobjective lens 71 is moved to a prescribed position. Therefore, a laserbeam having the wavelength of 780 nm emitted from laser element 68passes through objective lens 71 and is focused on CD-R signal recordingsurface 28. Since CD-R allows writing once, it is possible that opticalpickup device 66 records signals by using the laser beam having thewavelength of 780 nm. Except these points, the operation is similar tothat of optical pickup device 10 shown in FIG. 2. Therefore, descriptionthereof is not repeated.

Eleventh Embodiment

In the first to ninth embodiments above, signal recording region 48 isformatted in accordance with the CD standard and in the tenthembodiment, it is formatted in accordance with the CD-R standard.Alternatively, it may be formatted in accordance with the MO (magnetooptical) disk standard. Table 3 below shows DVD and MO disk standardsand conditions for reproduction.

                  TABLE 3    ______________________________________    Type            DVD         MO disk    ______________________________________    Standard Substrate   0.6 mm      1.2 mm             Thickness   (0.55-0.65 mm)                                     (1.1-1.3 mm)             Shortest    0.40 μm  0.25 μm             Pit Length (0.3-0.5 μm)                                    (0.20-0.30 μm)             Track Pitch                         0.74 μm 0.7 μm                        (0.73-0.75 μm)                                    (0.5-0.8 μm)             Reflectance                        at      20-40%                                      at least                        least         15-25%                        70%    Condition             Spot        0.9 μm  1.1 μm    for      Diameter   (0.85-0.95 μm)                                    (0.8-1.2 μm)    Reproduction             Numerical  0.60        0.55             Aperture   (0.55-0.65) (0.50-0.60)             Wavelength 635 nm      680(665-695) nm                        (620-650) nm                                    or                                    780(765-795) nm    ______________________________________

As is apparent from the table, according to the MO disk standard, theshortest domain length is 0.25 (tolerance ±0.05) μm, track pitch is 0.7(0.5-0.8) μm and reflectance is higher than 15-25%.

The signal recording region formatted in accordance with the MO diskstandard includes a recording layer formed on a transparent substrateand a reproduction layer formed on the recording layer. Preferably, itfurther includes a non-magnetic layer formed between the recording layerand the reproduction layer. Recording layer is formed of (1) TbFeCo, (2)an alloy of one selected from the group consisting of Fb, Gd, Dy, Nd andHo and one selected from the group consisting of Fe, Co and Ni, or (3) amulti-layered film. The reproduction layer is formed of one selectedfrom the group consisting of GdFeCo, GdFe, GdCo and R₃ Fe₅ O₁₂ (R=Y or arare earth element). The non-magnetic layer is formed of an alloyincluding at least one selected from the group consisting of SiN, AlN,TiN, SiO₂, Al₂ O₃, SiC, TiC, ZnO, SiAlON, ITO, SnO₂, and Al.

DVD/MO disk compatible optical pickup device is structured in thesimilar manner as DVD/CD-R compatible optical pickup device 66 shown inFIG. 16. At the time of recording and/or reproducing of an MO disk,laser beam having the wavelength of 680 or 780 (tolerance ±15) nm isgenerated by laser element 68, and objective lens 71 having numericalaperture of 0.55 (tolerance ±0.05) is moved to a prescribed position.Other operations are the same as described above. Therefore, descriptionis not repeated.

Twelfth Embodiment

The first to eleventh embodiments above are directed to an optical diskfor checking compatibility of two different optical disks. The twelfthembodiment relates to an optical disk for checking compatibility amongthree different optical disks. An optical pickup device 72 shown in FIG.17 is capable of reproducing DVD, CD and CD-R. Optical pickup device 72includes, in addition to the structure of DVD/CD compatible opticalpickup device 10 shown in FIG. 2, another objective lens 71 as in theDVD/CD-R compatible optical pickup device 66 shown in FIG. 16.

When a DVD is reproduced, laser element 67 generating a laser beamhaving the wavelength of 635 nm is activated, objective lens 70 is movedto a prescribed position, and a voltage is applied to transparentelectrode 32 of plane of polarization rotating unit 22. Consequently,similar to DVD/CD compatible optical pickup device 10 shown in FIG. 2,the laser beam is focused on DVD signal recording surface 27.

When a CD is reproduced, similar to reproduction of DVD described above,laser element 67 generating a laser beam having the wavelength of 635 nmis activated and objective lens 70 is moved to a prescribed position.However, voltage is not applied to transparent electrode 32 of plane ofpolarization rotating unit 22. Consequently, similar to DVD/CDcompatible optical pickup device 10, the laser beam is focused on CDsignal recording surface 28.

When a CD-R is reproduced, laser element 68 generating a laser beamhaving the wavelength of 780 nm is activated, objective lens 71 is movedto a prescribed position and a voltage is applied to transparentelectrode 32 of plane of polarization rotating unit 22. Consequently,the laser beam which is polarized in a direction parallel to the sheetemitted from laser element 68 is transmitted with its plane ofpolarization not rotated by plane of polarization rotating unit 22.Therefore, similar to the DVD/CD-R compatible optical pickup device 66shown in FIG. 16, the laser beam is focused on CD-R signal recordingsurface 28.

In order to check whether or not the optical pickup device 72 is capableof reproducing DVD, CD and CD-R, optical disk 72 in accordance with thetwelfth embodiment shown in FIG. 18 includes, in addition to DVD signalrecording region 43 and CD signal recording region 48, a signalrecording region formatted in accordance with the CD-R standard(hereinafter referred to as "CD-R signal recording region") 74. CD-Rsignal recording region 74 is formed in the same plane as CD signalrecording region 48. Therefore, distance between CD-R signal recordingregion 74 and main surface 71 is the same as the distance between CDsignal recording region 48 and main surface 41. CD-R signal recordingregion 74 includes a recording film 75 including cyanine dye formed onultraviolet curing resin 49. Recording film 75 of CD-R signal recordingregion 74 allows recording of signals once.

As shown is FIG. 19, DVD signal recording region 43 is formed on theinnermost periphery of optical disk 73. CD signal recording region 48 isformed overlapping the DVD signal recording region 43 on the innerperiphery of optical disk 73. CD-R signal recording region 74 is formedon the outer periphery of optical disk 73.

In order to check compatibility of optical pickup device 72 shown inFIG. 17 by using optical disk 73 having the above described structure,first, DVD signal recording region 43 is irradiated with a laser beamfrom optical pickup device 72, and whether or not a signal from DVDsignal recording region 43 can be reproduced by optical pickup device 72is determined. Thereafter, optical pickup device is moved from DVDsignal recording region 43 to CD signal recording region 48. Thereafter,CD signal recording region 48 is irradiated with a laser beam fromoptical pickup device 72, and whether a signal from CD signal recordingregion 48 can be reproduced by optical pickup device 72 is determined.Thereafter, optical pickup device 72 is moved from the CD signalrecording region 48 to CD-R signal recording region 74. Finally, CD-Rsignal recording region 74 is irradiated with laser beam from opticalpickup device 72, and whether a signal from CD-R signal recording region74 can be reproduced by optical pickup device 72 is determined. Thoughthe order of checking is DVD, CD and CD-R here, it is not limited tothis order.

According to the twelfth embodiment, optical disk 73 includes DVD signalrecording region 43, CD signal recording region 48 and CD-R signalrecording region 74. Therefore, by using only one optical disk 73, it ispossible to check whether optical pickup device 72 is capable ofreproducing DVD, CD and CD-R.

Here, DVD signal recording region 43, CD signal recording region 48 andCD-R signal recording region 74 are formed in this order from the innerto outer periphery. However, these may be formed in opposite order.Alternatively, CD signal recording region 48 may be formed on the outerperiphery, and CD-R signal recording region 74 may be formed on theinner periphery, overlapping DVD signal recording region 43.

Thirteenth Embodiment

Though CD signal recording region 48 is formed overlapping DVD signalrecording region 43 in the twelfth embodiment above, the overlappingregion is unnecessary. Therefore, it may be removed by patterning, as inan optical disk 77 in accordance with the thirteen embodiment shown inFIG. 20.

Fourteenth Embodiment

In the twelfth embodiment shown in FIG. 18, DVD signal recording region43 is formed only on the inner periphery. However, it may be formed onthe entire surface of optical disk 78 in accordance with the fourteenthembodiment shown in FIG. 21. Here, DVD signal recording region 43 isformed on the inner periphery and CD-R signal recording region 74 isformed on the outer periphery. However, CD signal recording region 48may be formed on the outer periphery and CD-R signal recording region 74may be formed on the inner periphery.

Fifteenth Embodiment

In the twelfth embodiment shown in FIG. 18, transparent substrate 42 isformed of glass so as to improve durability. However, it may be formedof a polysilicon resin, as in an optical disk 79 in accordance with thefifteenth embodiment shown in FIG. 22.

Sixteenth Embodiment

Though twelfth to fifteenth embodiments above are directed to an opticaldisk for single layer DVD, the sixteenth embodiment is directed to anoptical disk of two layer DVD. Referring to FIG. 23, in an optical disk80 in accordance with the sixteenth embodiment, DVD signal recordingregion 43 includes a first signal recording layer 59, a transparentintermediate layer 62 and a second signal recording layer 60.

Seventeenth Embodiment

In the sixteenth embodiment, CD signal recording region 48 is formedoverlapping signal recording layers 59 and 60 of DVD signal recordingregion. However, the overlapping region may be removed as in an opticaldisk 81 in accordance with the seventeenth embodiment shown in FIG. 24.

Eighteenth Embodiment

In the sixteenth and seventeenth embodiments, the outer diameter of thefirst signal recording layer 59 is equal to the outer diameter of thesecond signal recording layer 60. However, the outer diameter of thefirst signal recording layer 59 may be smaller than the outer diameterof the second signal recording layer 60 as in an optical disk 82 inaccordance with the eighteenth embodiment shown in FIG. 25.

Nineteenth Embodiment

In the sixteenth embodiment shown in FIG. 23, transparent substrate 42is formed of glass. However, a transparent substrate 56 may be formed ofa polycarbonate resin as in an optical disk 83 in accordance with thenineteenth embodiment shown in FIG. 26.

Twentieth Embodiment

The twelfth to nineteenth embodiments above are directed to an opticaldisk for checking a DVD/CD/CD-R compatible optical pickup device 72.However, the present invention may be directed to an optical disk forchecking a DVD/CD/MO disk compatible optical pickup device 84 shown inFIG. 27. More specifically, an optical disk (not shown) in accordancewith the twentieth embodiment includes, in place of the CD-R signalrecording region 74 in accordance with the twelfth to nineteenthembodiments, a signal recording region formatted in accordance with theMO disk standard.

Here, an example of DVD/CD/MO disk compatible optical pickup device willbe described. The optical pickup device 84 includes, in place of laserelement 68 of optical pickup device 72 shown in FIG. 17, a laser element85 for generating a laser beam having the wavelength of 680 or 780(tolerance ±15) nm, and in place of objective lens 71 of optical pickupdevice 72, an objective lens 86 designed to focus a laser beam on asignal recording surface 28 of an MO disk and having a numericalaperture of 0.55 (tolerance ±0.05).

When an MO disk is reproduced, laser element 85 is activated, objectivelens 86 is moved to a prescribed position and a voltage is applied totransparent electrode 32 of plane of polarization rotating unit 22.Accordingly, in the similar manner as in reproducing a CD-R by theoptical pickup device 72, the laser beam which is polarized in adirection parallel to the sheet emitted from the laser element 85 istransmitted with its plane of polarization not rotated by plane ofpolarization rotating unit 22, and is focused on signal recordingsurface 28 of MO disk, through objective lens 86. Other operations arethe same as those in optical pickup device 72. Therefore, descriptionthereof is not repeated.

Other Embodiments

Table 4 below show types of signal recording regions which can be formedin the optical disk in accordance with the present invention.

                  TABLE 4    ______________________________________    1.2 mm thickness  0.6 mm thickness    ______________________________________    CD(-DA)           Single layer DVD    CD-ROM            Two layer DVD    CD-R              Single layer DVD-ROM    CD-RW             Two layer DVD-ROM    MO disk           DVD-R    PC disk           DVD-RAM    ______________________________________

As shown in the table, optical disks having the thickness of 1.2 mminclude CD(-DA), CD-ROM, CD-R, CD-RW (Compact Disk-Rewrite), MO disk andPC (Phase change) disk such as represented by a PD disk. Meanwhile,optical disks having the thickness of 0.6 mm include single layer DVD,two layer DVD, single layer DVD-ROM, two layer DVD-ROM, DVD-R (DigitalVideodisk-Recordable) and DVD-RAM (Digital Videodisk-Random AccessMemory).

In the first to ninth embodiments above, a combination of CD and singlelayer or two layer DVD has been described. In the tenth embodiment, acombination of CD-R and single or two layer DVD is described, in theeleventh embodiment, combination of an MO disk and single or two layerDVD is described, in the twelfth to nineteenth embodiments, acombination of CD, CD-R and a single or two layer DVD is described andin the twelfth embodiment, a combination of a CD, an MO disk and asingle or two layer DVD is described. However, the present invention isapplicable to optical disks having different combinations. According tothe optical disks shown as examples in Table 4, there is 36 (=6×6)possible combinations of optical disks having two different signalrecording regions. There is 90 (=₆ C₂ ×6) combinations for optical diskshaving three different signal recording surfaces. Further, combinationof optical disks not shown in Table 4 is also possible.

Although the present invention has been described and illustrated indetail, it is clearly understood that the same is by way of illustrationand example only and is not to be taken by way of limitation, the spiritand scope of the present invention being limited only by the terms ofthe appended claims.

What is claimed is:
 1. An optical recording medium,comprising:transparent substrates having respective main surfaces; afirst signal recording region formed in one of said transparentsubstrates substantially parallel to one of the respective main surfacesand formatted in accordance with a first standard; a first reflectionfilm formed on said first signal recording region on a side opposite tothe one of the respective main surfaces of said one of said transparentsubstrates; a second signal recording region formed in another one ofsaid transparent substrates substantially parallel to another one of therespective main surfaces and formatted in accordance with a secondstandard; and a second reflection film formed on said second signalrecording region on a side opposite to the another one of the respectivemain surfaces of said another one of said transparent substrates;whereinthe first and second signal recording regions respectively extend, alongthe respective main surfaces at different planes and lengths, in saidtransparent substrates thereof.
 2. The optical recording mediumaccording to claim 1, whereindistance between said first signalrecording region and the one of the respective main surfaces of said oneof said transparent substrates is shorter than distance between saidsecond signal recording region and the another one of the respectivemain surfaces of said another one of said transparent substrates.
 3. Theoptical recording medium according to claim 2, whereinsaid first signalrecording region is formed partially in said one of said transparentsubstrates, and said second signal recording region is formed entirelyin said another one of said transparent substrates.
 4. The opticalrecording medium according to claim 2, whereinsaid first signalrecording region is formed at least on an inner periphery in said one ofsaid transparent substrates, and said second signal recording region isformed at least on an outer periphery in said another one of saidtransparent substrates.
 5. The optical recording medium according toclaim 2, whereinsaid first signal recording region is formed at least onan outer periphery in said one of said transparent substrates, and saidsecond signal recording region is formed at least on an inner peripheryof said another one of said transparent substrates.
 6. The opticalrecording medium according to claim 2, whereinsaid first signalrecording region includes a first signal recording layer, a transparentintermediate layer formed on said first signal recording layer, and asecond signal recording layer formed on said transparent intermediatelayer.
 7. The optical recording medium according to claim 1, whereinsaidtransparent substrates are formed of glass.
 8. The optical recordingmedium according to claim 1, further comprising:a third signal recordingregion formed in yet another one of said transparent substratessubstantially parallel to yet another one of the respective mainsurfaces and formatted in accordance with a third standard; and a thirdreflection film formed on said third signal recording region on a sideopposite to the yet another one of the respective main surfaces of saidyet another one of said transparent substrates.
 9. The optical recordingmedium according to claim 8, whereindistance between said first signalrecording region and the one of the respective main surfaces of said oneof said transparent substrates is shorter than distance between saidsecond signal recording region and the another one of the respectivemain surfaces of said another one of said transparent substrates, anddistance between said third signal recording region and the yet anotherone of the respective main surfaces of said yet another one of saidtransparent substrates is substantially equal to distance between saidfirst or second signal recording region and the one or another one ofthe respective main surfaces.
 10. An optical recording medium,comprising:a first transparent substrate; a first signal recordingregion formed on said first transparent substrate and formatted inaccordance with a first standard; a first reflection film formed on saidfirst signal recording region; a second transparent substrate formed onsaid first reflection film; a second signal recording region formed onsaid second transparent substrate and formatted in accordance with asecond standard; and a second reflection film formed on said secondsignal recording region,wherein said first and second signal recordingregions formed on transparent substrates extend at different planes andlengths.
 11. A method of checking an optical pickup device by using anoptical recording medium including transparent substrates havingrespective main surfaces, a first signal recording parallel to one ofthe respective main surfaces and formatted in accordance with a firststandard, a first reflection film formed on said first signal recordingregion on a side opposite to the one of the respective main surfaces ofone of said transparent substrates, a second signal recording regionformed in another one of said transparent substrates substantiallyparallel to another one of the respective main surfaces and formatted inaccordance with a second standard, and a second reflection film formedon said second signal recording region on the side opposite to theanother one of the respective main surfaces of said another one of saidtransparent substrates, said method comprising the steps of:irradiatingsaid first signal recording region with a laser beam from said opticalpickup device for determining whether or not said optical pickup deviceis capable of reproducing a signal of said first signal recordingregion; after said step of irradiating, moving said optical pickupdevice from said first signal recording region to said second signalrecording region; and after said step of moving, irradiating said secondsignal recording region with a laser beam from said optical pickupdevice for determining whether said optical pickup device is capable ofreproducing a signal of said second signal recording region, wherein thefirst and second signal recording regions respectively extend, along therespective main surfaces at different planes and lengths, in saidtransparent substrates thereof.
 12. The optical recording mediumaccording to claim 1, whereinrecording density of said first signalrecording region (43) is higher than recording density of said secondsignal recording region (48).
 13. The optical recording medium accordingto claim 12, whereinshortest pit length of said first signal recordingregion (43) is shorter than shortest pit length of said second signalrecording region (48).
 14. The optical recording medium according toclaim 12, wherein track pitch of said first signal recording region (43)is shorter than track pitch of said second signal recording region (48).